I. Field of the Invention
This invention relates generally to medical apparatus for removing plaque and other deposits from the interior walls of a partially occluded blood vessel, and more particularly to the design of an atherectomy catheter whose cutting head exhibits a low profile to facilitate its being routed through the vascular system but which expands in use to effect removal of the atheroma.
II. Discussion of the Prior Art
The buildup of atheromas or the formation of thrombi in a blood vessel can cause serious circulatory problems and when complete blockages occur, distal tissues may be deprived of oxygen and nutrients leading to death of those cells distally of the blockage. Thus, the formation of an atheroma in a coronary artery can lead to a coronary infarction, especially when the artery becomes so narrowed by the plaque build-up that a tiny clot or thrombus cannot pass. Similarly, an atheroma or other type of stenotic lesion in a peripheral vein or artery can have a corresponding affect on tissue and cells supplied by the blocked blood vessel.
The treatment of such a condition naturally depends upon the location or site of the blockage. In the case of a blocked or partially blocked coronary artery, it has been the practice to conduct open-heart surgery wherein the blocked vessel is by-passed with an autograft. Similarly, blood vessel shunts have been installed in other body areas as well. Such surgery, however, tends to be quite traumatic involving opening the patient's chest and pericardium in the case of coronary by-pass surgery or extensive excision and vessel replacement in the case of other peripheral blockages.
More recently, following the technique created by A. Grunzig, a balloon catheter may be used to restore patency to a blood vessel without extensive surgery. A catheter having a small inflatable balloon on its distal end may be routed through the vascular system to the site of the constriction or blockage and when the deflated balloon is appropriately positioned to span the blockage, a fluid may be introduced into the proximal end of the catheter to inflate the balloon to a sufficiently high pressure whereby the blockage may be spread open and patency restored.
As in pointed in the Auth U.S. Pat. No. 4,445,509, there are certain deficiencies in the Grunzig procedure which render it ineffective in certain applications. For example, the blockage may be such that it is not possible to safely force the distal tip of the catheter through the blockage prior to the inflation of the balloon. In such a situation, it would be desirable if one could safely "tunnel" through the blockage using an appropriate cutting tool. Once a passage has been formed during such tunneling operation, a balloon can be advanced into the occlusion until it is totally across it. Once so positioned, the balloon can be inflated and the angioplasty procedure completed.
In U.S. Pat. No. 4,784,636 to Rydell and assigned to applicant's assignee, there is described a balloon atherectomy catheter comprising three concentrically disposed flexible plastic tubes. The innermost tube has an annular cutter secured to its distal end and secured to the proximal end of that catheter is a device which allows both rotational and translational motion to be imparted to that innermost tube. The cutter member is especially designed to preferentially remove tissue deposits directly in line with the cutter without producing significant lateral cutting.